The World-Wide Web (the Web) is a collection of formatted hypertext pages located on numerous computers around the world that are logically connected by the Internet. The Web has become a valuable resource for information relating to almost any subject, including entertainment, business, travel, and education, to name just a few. Web browsers, software providing user interfaces to the Web, allow individuals to access Internet content from personal computers. Internet terminals, such as those pioneered by WebTV Networks, Inc., of Mountain View, Calif., have made the Web accessible to an even larger segment of the population by providing access to the Web without the use of a personal computer. Internet terminals (also commonly referred to as set-top boxes) provide individuals with access to Web pages using an ordinary television (TV) set as a display and a remote control or wireless keyboard for user input.
Many Web sites include content relating to popular television programs, specific episodes, and their characters, for example. It would be desirable to provide a mechanism for integrating broadcast television programming with the Web to facilitate the retrieval and viewing of this and other content concurrently with the television broadcast or at a later time at the option of the viewer. In particular, it would be desirable to provide a practical mechanism for communication of logical addresses, such as Uniform Resource Locators (URLs), for Internet content relating to a television broadcast, for example, as part of the television signal.
The Electronic Industries Alliance (EIA) has published a standard relating to embedding data in line 21 of the vertical blanking interval (VBI) of a National Television Standards Committee (NTSC) video signal entitled, “Recommended Practice for Line 21 Data Service,” approved Sep. 20, 1994 (hereinafter “EIA-608”). EIA-608 describes various data services, such as closed captioning, text services, and extended data services (XDS) that are carried in line 21 of the VBT of an NTSC video signal. Details regarding these services can be found in EIA-608 which is incorporated herein by reference.
One approach that has been suggested for transmitting URLs as part of an NTSC video signal is to embed URLs in the Extended Data Service (XDS) channel. However, this approach has several limitations. For example, XDS packets are limited to 32 bytes including packet overhead. Since URLs and data associated therewith will typically exceed 32 bytes, this data would have to be spread over multiple XDS packets. Additionally, if URLs were to be transmitted in XDS packets they would compete for the limited bandwidth available to XDS with V-Chip program rating information. Bandwidth available to XDS may at times be insufficient to fully support both URLs and V-Chip rating information. Another problem with this approach is the difficulty associated with having more than one “active” URL for a program at the same time. This problem stems from (1) the difference between URLs and attributes that are typically associated with a program by way of XDS, such as a scheduled start time, a duration, an elapsed time, a program title, etc. and (2) the repetitive nature of XDS packets. Typically, only the most recently received attribute of a program is active. For example, an earlier elapsed time value associated with a particular program is replaced by a subsequently received elapsed time value associated with that program. In contrast, such behavior is undesirable for URLs as it may often be beneficial to have multiple URLs active at a given time during a program.
With regard to the repetitive nature of XDS packets, EIA-608 recommends transmitting XDS packets continuously to fill all available bandwidth beyond what is used by the captioning and text services and suggests repetition rate algorithms based on packet priorities. Briefly, as XDS usage increases, the repetition rate for each of the types of packets is decreased and XDS packets of the same type (e.g., those having the same packet ID) may be deleted by downstream encoders to accommodate the additional XDS traffic. Therefore, the only way to guarantee reception by the viewer of multiple URLs per television program is to provide unique packet IDs for each URL to assure they are not deleted as more of the XDS bandwidth is consumed downstream. However, coordinating such unique packet IDs among the many potential originators of URLs is not practical.
In light of the foregoing, what is needed is a more intelligent mechanism for communicating logical addresses associated with local and/or remote content within a video signal. In particular, it is desirable to accommodate the need for multiple active URLs at a given time during a TV program. Additionally, it is desirable to provide for improved error detection. Further, it is advantageous to choose a portion of the video signal which does not compete directly for bandwidth with V-Chip rating information, Finally, it is desirable to utilize a syntax that is suitable for a broad set of devices.